Microstructue and zinc corrosion mechanism of laser cladding Co-based alloy on 316L stainless steel

Co-based alloy coating was prepared by using semiconductor laser on the surface of 316L stainless steel. The microstructure, chemical composition, constituent phases and zinc corrosion mechanism of the laser cladding coating has been systematically studied. The results showed that with optimum process parameters of laser irradiation, the crack-free cladding coating with good metallurgical bond to the substrate and flat surface could be obtained. Co-based alloy cladding coating was mainly composed of γ-Co, M₂₃C₆ (M=Cr, Co, Fe) and the laves phases Co₃Mo₂Si of excellent corrosion resistance and hard wear-resistance phase Co₆W₆C. Liquid molten zinc corrosion tests at 460℃ showed that zinc corrosion mechanism of Co-based alloy cladding coating was a selective erosion. Corrosion transition region appeared on cladding surface in the color of bright white. Co-based solid solution matrix is preferably corroded at the transition region, which leads to spalling of laves phases. Therefore, the liquid zinc contributed to corrosion for the Co-based alloy cladding coating.